User cache and VPN

I have been having problems with VPN freezing up after 30 minutes. It has forced me to roll back to Leopard. That seems to have helped a great deal. Now it doesn't seize up til nearly two hours have passed. I was wondering if maybe there was a user cache that was filling up and forcing VPN to freeze. As soon as I disconnect the VPN all returns to normal. Maybe I should flush the user caches before I connect the VPN.